1. Field of the Invention
This application relates to an audio plug detection structure and method thereof, and more particularly, to an audio plug detection structure and method thereof by utilizing a time-varying signal as a detection signal.
2. Description of the Related Art
When an audio plug, such as a 3-pole audio plug or a 4-pole audio plug, is inserted into a corresponding audio jack, the audio jack needs to have a function to detect the audio plug in order to appropriately adjust the audio signal output. In other words, the audio signal output can remain low when the audio plug is not inserted into the audio jack, and switch to an appropriate output mode when the condition that the audio plug is inserted into the audio jack is confirmed, which can lower the electricity consumption in circuit and reduce the cost.
To detect the state whether the audio plug is inserted into the audio jack or not, an elastic and conductive connection point connected a power source can be disposed at the inside of the audio jack. The elastic and conductive connection point also corresponds to a ground terminal. When the audio plug is not inserted into the audio jack yet, the elastic and conductive connection point and the ground terminal are open. When the audio plug is being inserted into the audio jack, the frond end of the audio plug presses the elastic and conductive connection point to make it be in contact the ground terminal, and thus the elastic and conductive connection point and the ground terminal are closed and a current can flow therebetween. According to such current or a voltage variation relating to such current, whether or not the audio plug is inserted into the audio jack can be detected. However, this method cannot tell if the inserted object is the audio plug. For example, when a plug of a cell phone strap or a dust plug is inserted into the audio jack, the elastic and conductive connection point is still pressed and the generated current may cause a mistake.
Therefore, a typical method is to dispose a detection circuit with the connection point for detection on the audio jack. Please refer to FIG. 1, which shows the structure of a typical audio jack. In FIG. 1, the audio plug 20 includes four pole points, a first pole point 21, a second pole point 22, a third pole point 23, and a fourth pole point 24. After the audio plug 20 is inserted into an audio jack 10, the first pole point 21, the second pole point 22, the third pole point 23, and the fourth pole point 24 are connected to a left channel output terminal HP_L, a right channel output terminal HP_R, a ground terminal, and a microphone input terminal MIC_IN of an audio chip 30 via a first connection point 11, a second connection point 12, a third connection point 13, and a fourth connection point 14 of the audio jack, respectively. There is a detection connection point 15 disposed at a position opposite to the first connection point 11 inside the audio jack 10. The detection connection point 15 is connected to a detection terminal JD of the aforementioned audio chip 30 as well as a DC voltage source VDD. Specifically, before the audio plug 20 is inserted into the audio jack 10, the detection connection point 15 and the first connection point 11 are open, where a high voltage substantially the same as the voltage provided by the voltage source VDD is input into the detection terminal JD. After the audio plug 20 is inserted into the audio jack 10, the detection connection point 15 and the first connection point 11 are closed by the metal material of the first pole point 21, and the voltage input into the detection terminal JD is pulled down, which can be used to determine that the audio plug 20 has been inserted into the audio jack 10.
However, in both the above described methods, there are connection points disposed inside the audio jack and specifically used to detect whether or not the audio plug is inserted into the audio jack. Those connection points and the circuits connected thereto occupy extra space in the whole circuit, and the flexibility for circuit or device structure design may decrease. Besides, the aforementioned structures or methods require a DC voltage source connected to the detection connection point, and the electricity consumption may increase and cause the cost increasing as well.